Web tension isolator or amplifier for web handling apparatus

ABSTRACT

A web tension isolator or amplifier includes a rotatable pulley engageable with a driver pulley in response to tension forces in a web that is wrapped on the driven pulley. The mechanism maintains the film tension ratio (i.e., the ratio of the tensions in the web portions on the two sides of the driven pulley) substantially constant regardless of the magnitude of the web tension. The mechanism automatically and quickly adjusts the web tension for any variations in the tensions of the web portions at either side of the driver pulley. The mechanism can be used (for example) in a motion picture projector between the film gate and a supply reel and/or a take-up reel.

United States Patent Morse [s41 wEB TENSION lsoLAToR 0R AMPLIFIER FORWEB. HANDLING APPARATUS [72] lnventor: John E. Morse, Rochester, NY.[73] Assignee: Eastman Kodak Company, Rochester,

NY. A

1151 3,656,674 1451 Apr. 18, 1972 Bretti ..226/l88 X PrimaryExaminer-Allen N. Knowles Attorney-Robert W. Hampton and G. HermanChildress 57 ABSTRACT A web tension isolator or amplifier includes arotatable pulley engageable with a driver pulley in response to tensionforces in a web that is wrapped on the driven pulley. The mechanismmaintains the film tension ratio (i.e., the ratio of the tensions in theweb portions on the two sides of the driven pulley) substantiallyconstant regardless of the magnitude of the web tension. The mechanismautomatically and quickly adjusts the web tension for any variationsinthe tensions of the web portions at either side of the driver pulley.The mechanism can be used (for example) in a motion picture projectorbetween the film gate and a supply reel and/or a take-up reel.

8 Claims, 9 Drawing Figures .PATENTEMPRWIQYE 9,656,674

SHEET 1 OF 4 2 230 I, ITT'"- TITIITT in/ a II 1' u :w 1

r r A b JOHN E. MORSE f INVENTOR. 22

ATTORNEYS PATENTEUr-FR 18 1972' SHEET 2 OF 4 JOHN E. MORSE 4 INVENTORfwd/M ATTORNEYS FATENTEBAPR 18 1972 SHEET 3 OF 4 FIG. 40

JOHN E. MORSE INVENTOR BYJQLQ m ATTORNEYS PATENTEDAPR 18 1972 SHE ET 0F4 JOHN E. MORSE IN VENTOR BY 241% m fwd/156.

ATTORNEYS WEB TENSION ISOLATOR OR AMPLIFIER FOR WEB HANDLING APPARATUSBACKGROUND OF THE INVENTION control is desirable in feeding of varioustypes of webs or web-- like members, such as film, magnetic tapes,belts, chains and the like. However, this problem is particularlytroublesome in connection with a web advancing mechanism thatintermittently advances a thin, flexible web, e.g., a motion pictureprojector, wherein it is important for pro'ection of a steady image thatthe film while in a projector film gate be held substantiallystationary. In order for the film to be stationary in the gate it shouldbe substantially isolated from those film tensions and tensionfluctuations produced by normal operation of the projector. Motionpicture projectors produce undesirable film tensions on film at thefilmgate in various ways. For example, the film take-up reel is usuallyconstantly driven ina take-up direction'through a friction or so-calledtendency drive even when the film is being held stationary in the gate.The film supply reel also may be driven in a take-up direction by afriction or tendency drive even when film is being forcibly withdrawnfrom the supply reel by operation of the claw. Even if the supply. reelis freewheeling, tension fluctuations are produced by the mass of thereel and film wound thereon opposing advancement of the film by thepull-down claw. Tension fluctuations attributable to the mass of thereel and film are particularly acute when large film rolls (e.g., 400feet of film) are to be handled by the projector. Thus a strip of filmbeing projected by a motion picture projector is constantly subjected totension forces that tend to produce undesirable unsteady projectedimages due to slight film movement at the gate when the film should beheld stationary. In addition, these tension forces adversely affect filmlife. Various means have been proposed in the past for avoiding theseproblems but, for one reason or another, most of the prior. arrangementshave failed to adequately or completely solve the problem.

SUMMARY OF THE INVENTION Accordingly, it is an object of this inventionto improve web handling apparatus by controlling the tension forces inportions of the web.

Another object of the invention is to provide a webtension amplifiercapable of maintaining substantially constant a predetermined or designtension force in a web strand.

A more specific object of the invention is to isolate film at aparticular portion of a film advancing mechanism from tension forcesacting on the film in other portions of the film advancing mechanism.

A still further object of the invention is to isolate film while in thefilm gate of a motion picture projector from tension forces produced atthe supply and take-up reels,and at other portions of the mechanism.

In accordance with the present invention, a length of web material iswrapped at least partially around a rotatable pulley or the like, andfluctuations in tension in the web strands at either side of the pulleycouple and uncouple the pulley from a driving connection with a drivermember. The geometry and arrangement of the parts 'is such that theextent of the drive applied to the web supporting member is a functionof tension forces in the web portions adjacent the driven pulley so thatthe tension forces in such web portions can be accurately controlled.

In accordance with specific illustrative embodiments of the invention, afreely rotatable pulley is mounted on a pivoted arm. A driver pulley ismounted for rotation about a fixed axis and the surface of the firstpulley is brought into contact with Y the driver pulley by tensionforces in portions of a strip of film '13 for pivotal movement of the 2wrapped partially around the first pulley. The forces applied and themechanical geometry of the mechanism are such that the film tensionratio, i.e. the ratio of the tensions in the film on the respective twosides of the pulley, is maintained substantiallyconstant regardless ofthe magnitude of the film tension or the driver pulley velocity. Two ofthe mechanisms can be provided in a single motion picture projector'andsymmetrically positioned one on each side of the film gate to isolatefilm in the film gate from film tension fluctuations.

The invention, and its objects and advantages, will become more apparentin the detailed description of the preferred embodiments presentedbelow.

BRIEF DESCRIPTION OF THE DRAWINGS In the detailed description of thepreferred embodiments of the invention presented below, reference ismade to the ac companying drawings, in which:

FIG. 1 is a schematic view of -a web tension isolator or amplifier inaccordance with a specific illustrative embodimentof the invention;

FIG. 2 is an elevation of a with the present invention;

FIG. 3 is a schematic view of certain portions of a motion pictureprojector including tension isolators or amplifiers in accordance withthe present invention;

FIG. 4 is a schematic view of a modification of the isolator of FIG. 1wherein an internal friction disk driver is utilized;

FIG. 4a is a section taken along line 4a-4a in FIG. 4.

FIG. 5 is a schematic view of a modification of the isolator of FIG. 1wherein the arm for the pulley is utilized to impart additional torqueand increase the overall gain of the system;

FIG. 6 is a view of a modification somewhat similar to FIG. 5 bututilizing a differently shaped pivoted arm;

FIG. 7 is a schematic view of still another modification wherein thepivoted arm has been eliminated; and

FIG. 8 is a view of an embodiment wherein a drive belt is used insteadof a driver pulley or disk.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Because web handling apparatusare well known, the present description will be directed in particularto elements forming part of, or cooperating more directly with,the'present invention, elements not specifically shown or describedherein being understood to be selectable from those known in the art.

The terms tension isolator and tension amplifier" are usedinterchangeably in this description in view of the dual by relatedfunctions achieved by the mechanisms described. Referring now to thedrawings and first particularly to FIG. 1, a tension isolator oramplifier in accordance with one specific illustrative embodiment of theinvention comprises a freely rotatable pulley 11 mounted at one end ofan arm 12. A web is engageable with an angular portion of pulley 11 asexplained later. The arm is mounted at its other end on a support orbase arm and pulley 11 in both directions about an axis X. A driverpulley 14 is continuously rotated about a fixed axis by suitable powermeans (not shown in FIG. 1). The pulleys 11 and 14 are mounted withrespect to each other so that the outer surface of pulley 11 at a radiusR, can be brought into engagement with the surface of pulley 14 topermit pulley 11 to be driven by pulley 14. Driver pulley 14 ispreferably driven at a speed which is sufficiently high so that slippagecontinuously occurs between the surfaces of the driver and the drivenpulleys when they are in contact. The

pulley of one type suitable for use driving torque of pulley ll depends(in part) on the force urgproduced by the pulley system.

Under the influence of the forces or vectors T and T acting on the hightension side and low tension side, respectively, of

the film l7, pivoted arm 12 may be swung about its axis until thesurface of pulley 11 at radius R is brought into contact with thedriving surface of pulley 14. The contact force between the two pulleyscan increase in response to increases in vectors T and/or T untilequilibriumis reached between the forces acting on the mechanism. InFIG. 1 the forces acting on pulley 11 when the system is in equilibriumare as represented by vectors A, B and C. Vector A is the resultant ofthe radial and tangential forces imposed on pulley 11 by pulley 14. Thedirection of vector A, referred to herein as the driver line of action,is determined by the coefficient of sliding friction t between thedriver pulley l4 and the driven surface of pulley 11 at the point atwhich pulley 11 contacts pulley 14. Vector B represents the'forceexerted on pulley 11 by the pivoted arm 12, which force acts along thecommon center line or axis of the pulley and the arm when thegeometrical relation between the parts is as shown in FIG. 1. Vector Crepresents the resultant line of action of the total forces (the tensionforces T, and T exerted by film 17 on pulley 11. From the foregoing itwill be apparent that an increase in the film tension (vector C)produces an increase in the driving force (vector A) applied to pulley11 by pulley 14, and that such increase must be balanced by vectors Aand B for the system to remain in equilibrium.

The lines of action of vectors A and B intersect at a point 0. Thelocation of point Q is a function of the mechanical geometry of themechanism and the driver coefficient of friction only. When pulley 11 isin rotational equilibrium, the line of action of vector C also passesthrough the point Q. Vectors T and T intersect at a point S.Accordingly, the total film force line of action (vector C) also passesthrough point S.

From the preceding discussion, it follows that the location anddirection of the total film force line of action (vector C) isestablished solely by the geometry of the mechanism and the drivercoefficient of friction. The ratio T /T comprises the film tension ratioor gain" of the mechanism. Since the direction of vector C isestablished, the ratio TJT also is established for a givenposition ofthe two film strands or portions at opposite sides of pulley ll.

When pulley 11 is in translational equilibrium, the A and B forcesadjust themselves so that vectors A, B and C add vectorially to zero.Thus, any increase in film tension (vector C) increases the vectorforces designated A and B but does not change the T /T ratio. Thistension ratio remains constant regardless of the magnitude of the filmtension or speed of pulley rotation as long as the coefficient ofsliding friction between pulleys 11 and 14 does not change. Also, achange in the direction of the line of action of any of vectors A, B andC can be compensated for by changes in the other vector(s) to provide anequilibrium condition.

In general the tension ratio T /T or gain" of a tension isolator oramplifier of this invention is determined by: a. The coefficient ofsliding friction u;

b. The ratio R /R c. The angle formed by a line from axis X to thecenter of pulley 11 and a line through the point of contact betweenpulleys 11 and 14 and the center of the pulley l1; and

d. The location of the film wrap arc, i.e., the location of that portionof the pulley 11 at radius R that is contacted by By variousarrangements and combinations of the basic elements discussed above, theoperating characteristics of the isolator or amplifier of this inventionmay be varied.

As previously mentioned, during operation the web or film 17 should notslip with respect to the driven pulley 11. This no-slip condition iseasily achieved in a number of different ways. For example, a V-groovetype pulley generally surface 22 that comprises a root support. Thesupport 22 is positioned between two spaced and oppositely taperedfrustoconical surfaces 23a and 2312. These surfaces are contacted by theside edges of the film throughout the extent of the wrap angle of thefilm about the driven pulley. Surfaces 23a and 23b are inclined at equalangles a and b, and these angles are preferably 'sufiiciently small sothat no slippage will occur between the side edges of film l7 and thesurfaces 23a and23b contacted by the film. Ordinarily the root support22 is not contacted by the film, but it is'preferably closely adjacentto the inner surface of film 17 so that it can be contacted by the filmin the event the film buckles inwardly, thereby eliminating excessivetensions that otherwise might be encountered above the normal operatingrange of the mechanism of the invention. Normally the diameter ofportion 22 of the pulley is selected so that the clearance betweenportion 22 and the film is the minimum required to insure contactbetween the edges of the film and the tapered flanges or surfaces 23aand 23b. Since the film normally contacts the pulley 21 only along theside edges of the film, undesirable scratching and wear of the imageareas of the film is avoided.

' Various other means may be utilized for. preventing slip between thedriven pulley and the film 17. For example, when perforated film isbeing handled then the driven member 11 can be a sprocket having teethadapted to enter the film perforations. For either perforated film orunperforated film pulley 11 may be provided with a high friction surfaceor face. For example, a coating of rubber or'other elastomeric materialmay be provided'on the surface of the pulley contacted by the film. Ofcourse, when film or similar webs are to be handled by the mechanism,surfaces contacted by such webs should not be unduly abrasive. Otherconstructions of the driven member may be used depending upon theparticular application of the tension isolator vor amplifierapplication, the nature of the web or other material being handled, etc.

FIG. 3 illustrates schematically a motion picture projector comprising afilm gate 24 located along a film path between a roll of film on a filmsupply reel 27- and a take-up'device or reel 28. The projector has twosubstantially identical film tension isolators or amplifiers 40 and 50of the type described hereinbefore arranged symmetrically on oppositesides of gate 24. Each tension isolator has its low tension side towardfilm gate 24 and its respective high tension side toward supply reel 27and take-up reel 28, respectively.

The tension isolators are the same basic mechanisms and have the samebasic operating theory as previously described in connection with FIGS.1 and- 2. The supply amplifier or isolator 40 shown at the'right in FIG.3 comprises a rotatable pulley 41 mounted for free rotation in bothforward or reverse directions on an-arm 42 which is pivotally supportedon base 43. Arm 42 extends beyond its pivotal mounting on base 43, andthe extension is engaged by a tension spring 44. A driving roller orpulley 47 is rotatably supported on a fixed support or base 48 and iscontinuously rotated in the direction indicated by suitable power means,such as a motor M, coupled to pulley 47. Spring 44 is preferably a weakspring and it biases pulley 41 away from pulley 47. I

The take-up isolator or amplifier 50 shown at the left comprises arotatable pulley 51 mounted for rotation in both directions on an arm 52which is pivotally mounted on base 53. Pulleys 41 and 51 can beconstructed in the manner shown in FIG. 2 for pulley 21. An extension ofarm 52 is engaged by a weak biasing tension spring 54 that urges pulley51 away from a driver roller or pulley 55. Pulley 55 is rotatablysupported on 1 a fixed base 56 and is continuously rotated in thedirection indesignated 21 (FIG. 2) may be used as the driven pulley. Asshown in FIG. 2, the pulley may havea generally cylindrical 51.

dicated by suitable power means such as motor M. Drivers 47 and 55 areboth drivers at speeds that insure slippage between the drivers andtheir respective driven pulleys 41 and 51, and each driver is driven ina direction for feeding film toward the gate. Film 17 is wrappedpartially around pulleys 41 and 51. There should be no slippage betweenthe film and pulleys 41,

' not shown).

During advancement of film from reel 27 to reel 28, take-up reel 28 isdriven in a take-up direction by a so-called tendency driver, that is,the reel is driven through a friction clutch or the like at a ratehigher than the rate that film is delivered to the reel so that a pullis constantly maintained on the film. The clutching mechanism includedin the drive assembly permits the drive to be constantly applied to thereel even when no film ,is being taken up by reel 28. Similarly,

supply reel 27 may be tendency driven in a film take-up direction duringunwindingof film from the reel. A spindle suitable for use with supplyreel 27 is disclosed in US. Pat. No. 3,468,498 issued Sept. 23, 196.9 inthe name of L. .1. Hunting. Reels 27, 28 may be driven by spindles 27a,28a, respectively, that are coupled to motor M, as showndiagrammatically in FIG. 3.

A pair of lightly biased spring arms 73 and 74 can be provided at thelow tension sides of the film tension isolators between the film gate 24and driven pulleys 41 and 51, respectively. The spring arms are eachpivotally mounted on a stationary portion ofv the projector for pivotalmovement back and forth in the mannerindicated by the arrows in FIG. 3.Each arm has a finger portion shown at 73a'and 74a, respectively, whichengages and supports a portion of. the film strip between the respectivedriven pulley and the film 'gate.'The arms are spring biased away fromthe gate as illustrated diagrammatically so that a small tension orforce is exerted on the film. Thistension is inversely related to thesize of the film loop produced by the arms. Preferably, the spring forceacting on each arm has a natural frequency appreciably higher than themaximum pull-down frequency or rate of claw 58 so that the fingerportion of each arm remains in contact with the film at all times. Thespring force acting on anns 73, 74 is preferably obtained by makingthese arms of a spring material; however, separate spring members can beused if desired.

During operation of the projector for feeding film from the supply reel27 to the take-up reel 28, claw 58 effects intermittent motion of thefilm through the film gate 24. As a length of film is pulled from thesupply loop of film around finger 73a and added to the take-up looparoun'd finger 74a, the film loop supported by arm 73 ported by the arm74 becomes larger. Arms 73 and 74 are both'deflected to the left thechanges in the size of the film loops engaged by these arms. Filmadvancement therefor increases the force on the film between reel 27 andgate 24 and correspondingly decreases the film tension in the loopbetween gate 24 and reel 28. The tension isolators are effective tomaintain, a constant film tension ratio (T /T of to l, for example, inthe film loops around pulleys 41 and 51. Thus as the film tension in theloop of the supply amplifier increases, driving torque on pulley 41increases as theincreased film tension forces pulley 41 against drivepulley 47 with a greater force and thereby increases the effectivenessof the drive on pulley 41 from driver 47. The film is driven toward thegate and into the loop around arm 73 until the tension in that loopreturns to the design or equilibrium value. When such equilibriumcondition is reached, driver pulley 47 is ineffective to rotate pulley41. Conversely,

the film tension in the loop of the take-up tension isolator oramplifier first decreases due to the length of film fed toward pulley 51by claw 58, and driving torque on pulley 51 is decreased as pressurebetween rollers 51 and 55 is decreased, thus permitting take-up reel 28to pull film from the loop and restore the design or equilibrium filmtension in the portion of the film around pulley 51, thereby maintainingthe ratio T lTg constant. The above cycle of operation is repeated eachtime film is advanced toward the take-up reel.

(as viewed inFIG. 3) in response to becomes smaller and the film loopsup- I -77 and .left on the film at the gate.

' gentle stop by reingagement 'and 79c in which case reels 27 and 28 maybe a steadier projected image and increasing film life.

It will be noted that the overall arrangement of the projector partscontrolling film handling along the film path is fully symmetrical, andthat each tension isolator tends to drive film toward the film gate.Thus forward and reverse projection of film is basically the samealthough, of course, in opposite directions. The two tension isolatorsor amplifiers are fully symmetrical and the action of each is basicallythe same regardless of the direction of film movement. Thus reels 27 and28 have been arbitrarily designated as supply and take-up reels,respectively.

As previously noted, arm 42 may be biased counterclockwise by spring 44and arm 52 may be biased clockwise by spring 54. The biasing force ofeach spring is relatively light, preferably being just enough to movethe arm and disengage the supported pulley from the associated driverpulley at times when the reel film tension is extremely low. At suchtimes as pulley 51 or pulley 41 is so disengaged from its associateddriver, it then acts simply as a freely rotatable idler suitablelocation of the pulleys 41 and 51 the force of gravity may be used toeffect the biasing function of springs 44 and 54.

pulleys. This may be desirable during rewind (for example) so that oneor both of these pulleys act as free idlers. As shown in FIG. 3, thismay be accomplished by providing clutch levers 78 that can be swung inthe directions indicated to move arms 42 and 52 in directions that causethe respective driven pulleys supported by the anus to be disengagedfrom the pulleys 47 and 55. If desired, one pulley can be declutchedwhile the other pulley is driven in the normal way. Thus only pulley 41need be declutched to produce automatic rewinding .of film onto reel 27without further clutching of either reel 27 or 28. With .pulley 41acting as an idler, the full tension produced by reel 27 acts to theright on film at the gate. However, pulley 51 still being engaged causesonly one tenth (for example) of the tension produced by reel 28 to. acttoward the This difi'erence in film tension causes the film toaccelerate in a direction towards reel 27. This acceleration willcontinue until the motor drive speed of reel 27 or driver 55 isattained. The film can be brought to a of pulley 41- with driver 47which restores the tension balance. Correspondingly, pulley 51 may bedisengaged from driver 55 which will produce the same rewind action butin the opposite direction. It is understood that when rewinding orslowing the film at high speeds, the gate pressure pad, claw and anyother film restraining devices are normally retracted to allow unimpededmotion of the film. The described mechanism therefore can be seen toprovide a very simple means for control of all modes of film motion athigh and low speeds in either direction.

By way of further example, both clutch levers may be movedsimultaneously by means of a control lever 79 pivotal about an axis 79aand connected to both clutch levers by coupling means illustrateddiagrammatically in FIG. 3 at 79b clutched for high speed film motion ineither direction.

FIGS. 4-7 illustrate embodiments of tension isolators that are basicallysimilar in construction and theory of operation to the FIG. 1 embodimentpreviously described. In the embodiment shown in FIGS. 4 and 4a theexternal driver pulley 14 of FIG. 1 is omitted and a pulley 81 is drivenby an internal friction disk driver or pulley 82. Pulley 82 isengageable with a pulley. By

suitably generally cylindrical inner surface 85 that opens to at leastone end of pulley 81. The diameter of surface 85 is substantially largerthanthe diameter of pulley 82 so that pulley 81 is movable into and outof engagement with pulley 82. As before, pulley 81 is mounted on an arm83 for rotation in both directions,

and arm 83 is pivoted on a support or base 84. In this instance the film17 is wrapped on the outer surface of the pulley 81, and suitableprovision is made for a no-slip wrap. Driver or pulley 82 is mounted forrotation about a fixed axis and pulley 81 is brought into engagementwith the driver disk in response to the tension in the external paths offilm 17. The vectors and lines of action for the various forces involvedcan be plotted in the same manner described in connection with FIG. 1.The external configuration of pulley 81 may be the same as thatdescribed for pulley 21 (FIG. 2) and pulley 81 can be urged clockwiseout of contact with driver 82 by the force of gravity or by spring meansas described in connection with FIG. 3. I

In the embodiment shown in FIG. a pulley 101 (which may be similar topulley 21) is driven by driver pulley 102 in a manner generally similarto that described in the embodiment of FIG. 1. In this case, however,pulley 101 is mounted for rotation in both directions on one end of theshorter portion 1070 of an L-shaped arm or bell crank 107. An idlerroller 104 is mounted on the end of the longer portion 107b of the arm.

The film 17 is wrapped partiallyaround roller 104 and roller 101. Arm107 is pivoted on a support or base 108 at the intersection of armportions 107a and 107b.

- When used in a motion picture projector such as'shown i FIG. 3, arm107 is arranged so that roller 104 is located between the film gate andpulley 101. The L-shaped arm and the film wrap around part of roller 104in the manner shown provides a mechanical advantage that imparts anaddition torque to the pivoted arm which increases the overall tensionamplification or gain of the apparatus. Also, it reduces the effectiveinertia of the apparatus whichraises the frequency response of thetension amplifier or isolator system. This method of increasedamplification tendsto render the'apparatus less sensitive to changes ingeometry and coefficient of friction although the enhanced frequencyresponse amplifies the tension pulses produced during'film pull-down.

FIG. 6 shows a further embodiment that is generally similar to thatshown in FIG. 5. In FIG. 6,a pulley 111 is mounted on w an arm 112between the ends thereof for rotation in both directions. Arm 112 ispivotally mounted at one end on a support or base 113. Film 17 ispartially wrapped around a freely rotatable roller 117 which is mountedat the free end of arm 112. Pulley 111 is driven by a driver pulley 118in the manner previously described. In the FIG. 6 embodiment tensiongain of the apparatus results only from the pivoted ann extensionwhereas in the'embodiment of FIG. 5 the gain results both from the armextension and from the film tension situation.

In the embodiments of FIGS. 5 and 6 just described, the arm portionssupporting rollers 104 and 117 may be made of springmaterial. Also, inboth of these embodiments the effective inertia and hence the systemfrequency response is a function of the length and position of the armrelative to other parts of the mechanism.

In the embodiment illustrated in FIG. 7, the pivotally mounted arm hasbeen eliminated. A pulley 131 surrounds and is driven by an internaldriver disk 132 in a manner similar to that discussed in connection withFIG. 4. Driver 132 is drivenabout a fixed axis, and suitable retainers(not shown) may be provided for limiting axial movement of pulley 131.

action of the driver force on the pulley coincides with the line ofaction of the total film force on the pulley, and wherein the driverforce vector A is equal and opposite to the total film force vector C.Since the location of the point, of contact betweendriver disk 132 andpulley 131 is not rigidly fixed, the gain of the system depends upon theR lR ratio and the value of the coefficient of friction.

In the embodiments described hereinbefore, a separate disk ley aboutwhich the film or other web is wrapped. FIG. 8 illustrates an embodimentwherein the driver member comprises a driver belt 140 which is trainedabout a driven pulley member 142 at a radius R Belt 140 should have aslip type drive with respect to the pulley and the belt is driven at aspeed that tends to drive the pulley faster than the maximum speedrequired for advancing the film about the pulley. The pulley is providedwith a web supporting surface 144 at a radium R The belt and webengaging portions of the pulley are offset axially from each other. Film27 is wrapped about the pulley and engages surface 144. The pulley ismounted for rotation at the free end of an arm 146 and the other end ofthat arm is pivoted at 148 on a fixed support or base 150. In operation,the force of the engagement between the belt 140 and the pulley isdetermined by the tension in the film 17 and this, in turn, governs thedriving force imparted by the belt to the pulley.

While the invention has been described as applied particularly inconnection with film feeding mechanisms for motion picture projectors,it will be understood that the invention is applicable in connectionwith other types of webs, both perforated and non-perforated, belts ofvarious types, chain, etc. The preceding discussion has been directedprimarily to the use of the invention for maintaining a particularly lowtension force (T however, the invention is" equally applicable tomaintenance of a high tension force (T,) as, for example, in winding atight roll of web material. Irrespective of the application, simple andefficient means have been provided whereby the ratio of the tensions. ofthe web portions on opposite sides of the driven pulley is maintainedsubstantially constant by fully automatic means that are responsive tovariations in tension in the web portions themselves. This tension jratio and the magnitude of the tension forces designated T, and T may bevaried over a wide range, as desired, by different geometricalarrangements and combinations of the basic elements, and by changing thecoefficient of friction between the driver and driven pulley members. Itis also noted that the absence of film lubricant insures a highcoefficient of friction between the film and the driven pulley (which isdesirable) while the absence of lubricant is normally undesirable withprior film handling devices.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

1. In a motion picture projector having means for advancing film along afilm path from a film supply past a film gate to a film take-up, theprojector comprising two film tension isolators, each of said isolatorscomprising:

a film support member having a film driving surface adapted to havetrained there-around a loop of film, each isolator further comprisingfriction drive means for rotating said member, said isolators beingsymmetrically positioned along the film path at opposite sides of thefilm gate, and each of said isolators being effective to maintain apredetermined tension ratio in the portions of the film at oppositesides of the respective isolator whereby changes in tension forcesacting on the film due to advancement of film through the film gate fromthe film supply toward the film take-up are compensated for by saidisolators.

2. A projector as defined in claim 1 wherein each of said isolatorsfurther comprises means responsive to a variation in or pulley drivermember has been disclosed for driving a pulfrom said drive member abouta fixed axis; and

said film support member is carried by said arm for pivotal movementwith said arm, whereby said film support member is movable intoengagement with said drive member for rotation by said drive member.

5. A projector as defined in claim 1 wherein said friction drive meanscomprises an endless drive belt trained about a portion of said filmsupport member.

6. A projector as defined in claim 3 wherein:

said film support member has an opening therein defining a substantiallycylindrical surface; and

said. drive member is positioned at least partially within said openingand engageable with said surface for driving said film support member.

7. A motion picture projector or the like for advancing film along apath from a film supply through a film gate to a film take-up, theprojector comprising:

a rotatable member positioned along the film path and having a filmdriving surface around which a portion of said film can' be partiallywrapped so that film is advanced along the film path when said member isrotated; drive means for rotating said member, thereby to advance filmaround said member, said means for effecting a driving connectioncomprises (1) a substantially L-shaped arm having a first arm portion onwhich said rotatable member is supported and a second arm portion, (2) afilm guide member carried on. said second arm portion for guiding filmalong the film path adjacent to said rotatable member, and (3) meansmounting said am for pivotal movement about an axis spaced from saidrotatable member and extending through the arm substantially at theintersection of said am portions for permitting movement of saidrotatable member into and out of frictional driving engagement with saiddrive means.

8. A motion picture projector or the like for advancing film along apathfrom a film supply through a film gate to a film take-up, theprojector comprising:

. a rotatable member positioned along the film path and having a filmdriving surface around which a portion of said film can be partiallywrapped so that film is advanced along the film path when said member isrotated;

drive means for rotating said member, thereby to advance film aroundsaid member, said means for effecting a driving connection comprising(1) an arm mounted for pivotalmovement about one of its ends, (2) a filmguide member mounted on the other end of said arm and adapted to guidefilm along the film path adjacent to said rotatable-member, and (3)means for pivotally mounting said rotatable member on said am betweenits ends.

1. In a motion picture projector having means for advancing film along afilm path from a film supply past a film gate to a film take-up, theprojector comprising two film tension isolators, each of said isolatorscomprising: a film support member having a film driving surface adaptedto have trained there-around a loop of film, each isolator furthercomprising friction drive means for rotating said member, said isolatorsbeing symmetrically positioned along the film path at opposite sides ofthe film gate, and each of said isolators being effective to maintain apredetermined tension ratio in the portions of the film at oppositesides of the respective isolator whereby changes in tension forcesacting on the film due to advancement of film through the film gate fromthe film supply toward the film take-up are compensated for by saidisolators.
 2. A projector as defined in claim 1 wherein each of saidisolators further comprises means responsive to a variation in tensionforces acting on the film for controlling coupling of said frictiondrive means to said film support member.
 3. A projector as defined inclaim 2 wherein each of said friction drive means comprises: a drivemember mounted for rotation about a fixed axis; and means coupled tosaid drive member for constantly rotating said drive member about itsaxis.
 4. A projector as defined in claim 3 wherein: said means forcontrolling coupling of said friction drive means to said film supportmember comprises an arm mounted for pivotal movement in an arc towardand away from said drive member about a fixed axis; and said filmsupport member is carried by said arm fOr pivotal movement with saidarm, whereby said film support member is movable into engagement withsaid drive member for rotation by said drive member.
 5. A projector asdefined in claim 1 wherein said friction drive means comprises anendless drive belt trained about a portion of said film support member.6. A projector as defined in claim 3 wherein: said film support memberhas an opening therein defining a substantially cylindrical surface; andsaid drive member is positioned at least partially within said openingand engageable with said surface for driving said film support member.7. A motion picture projector or the like for advancing film along apath from a film supply through a film gate to a film take-up, theprojector comprising: a rotatable member positioned along the film pathand having a film driving surface around which a portion of said filmcan be partially wrapped so that film is advanced along the film pathwhen said member is rotated; drive means for rotating said member,thereby to advance film around said member, said means for effecting adriving connection comprises (1) a substantially L-shaped arm having afirst arm portion on which said rotatable member is supported and asecond arm portion, (2) a film guide member carried on said second armportion for guiding film along the film path adjacent to said rotatablemember, and (3) means mounting said arm for pivotal movement about anaxis spaced from said rotatable member and extending through the armsubstantially at the intersection of said arm portions for permittingmovement of said rotatable member into and out of frictional drivingengagement with said drive means.
 8. A motion picture projector or thelike for advancing film along a path from a film supply through a filmgate to a film take-up, the projector comprising: a rotatable memberpositioned along the film path and having a film driving surface aroundwhich a portion of said film can be partially wrapped so that film isadvanced along the film path when said member is rotated; drive meansfor rotating said member, thereby to advance film around said member,said means for effecting a driving connection comprising (1) an armmounted for pivotal movement about one of its ends, (2) a film guidemember mounted on the other end of said arm and adapted to guide filmalong the film path adjacent to said rotatable member, and (3) means forpivotally mounting said rotatable member on said arm between its ends.